1. Field of the Invention
The present invention relates to a wireless communication system. More particularly, the present invention relates to an apparatus and method for receiving a signal in the wireless communication system.
2. Description of the Related Art
A high-order modulation scheme is used for effective use of frequency resources. In this case, a receiver that uses coherent demodulation is generally necessary. Channel estimation is required for the coherent demodulation. For the channel estimation, a signal equally known to a transmitting end and a receiving end (e.g., a pilot signal) is transmitted from the transmitting end to the receiving end. Because the receiving end knows a Transmission (Tx) value of the pilot signal, channel estimation can be performed by using a Reception (Rx) value of the pilot signal.
An Orthogonal Frequency Division Multiplexing (OFDM)/Orthogonal Frequency Division Multiple Access (OFDMA) scheme primarily adopted in a 4th Generation (4G) communication system such as 3rd Generation Partnership Project Long Term Evolution (3GPP LTE), Worldwide Interoperability for Microwave Access (WiMAX), etc., can effectively handle a multipath through simple implementation. To increase spectral efficiency, the receiving end of the current communication system transmits the pilot signal to support the coherent demodulation.
A typical communication system transmits a signal in the following manner. Cyclic Redundancy Check (CRC) is used to detect an error that occurs in a transmission process, and Forward Error Correction (FEC) is used to correct the error. Channel-coded bits are subjected to rate matching to match to the number of modulation symbols allocated to each user, and thereafter mapped to a signal constellation. Then, a signal (e.g., a pilot signal, a reference signals, etc.) which is pre-known to the transmitting end and the receiving end and which is used for channel estimation is generated. An information signal and a pilot signal are deployed along a frequency axis, are converted into a time-axis signal by performing an Inverse Fast Fourier Transform (IFFT) operation, and are then transmitted.
In contrast to the aforementioned signal transmission process, a signal reception process is performed as follows. A time-axis signal is converted into a frequency-axis signal by performing a Fast Fourier Transform (FFT) on a signal received through an Rx antenna. An Rx signal corresponding to a position of the pilot signal is extracted, and a channel value of a position carrying data is estimated by using a channel component detected from the Rx signal. Thereafter, the Rx signal of the position carrying the data is demodulated and decoded on the basis of the channel estimation value.
As described above, coherent detection based on the pilot signal can be performed. Narrow-band interference having an effect in a subcarrier unit may be a concern during design and/or manufacture of user equipment. For example, narrow-band interference may occur due to power wiring, inadequate shielding, inadequate grounding of microphone or sensor cables, placement of the microphones or sensors near power lines or transformers, or the like. The narrow-band interference having an effect in the subcarrier unit may be referred to as ‘tone interference’. If the tone interference occurs at a position of the pilot signal, an error occurs in a channel estimation process, thereby causing significant performance deterioration. For example, in case of an LTE system, if the tone interference is present, the positions of the pilot signal and the tone interference coincide with each other with a probability of ⅙ in a one Tx antenna system, and the positions of the pilot signal and the tone interference coincide with each other with a probability of ⅓ in a two or more Tx antenna system.
Accordingly, there is a need for a method for improving performance deterioration caused by the tone interference in a wireless communication system that performs demodulation by using the pilot signal.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present invention.